You’re Probably Eating Too Much Protein: How Much is Too Much?

This article is an excerpt from the Shortform summary of "The China Study" by Colin Campbell. Shortform has the world's best summaries of books you should be reading.

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There’s a lot of confusion around protein. How much protein should I eat? Can you eat too much protein? If so, how much protein is too much?

Protein is an essential part of our biological makeup—proteins function as enzymes, hormones, tissues, and transport molecules, among other roles. But you probably don’t need as much protein as you’ve heard. We’ll cover how much protein you need, how much protein is too much, and what happens if you eat too much protein.

How Much Protein Should I Eat?

Protein is a chemical made up of chains of hundreds of amino acids. Our bodies need to replace proteins when they get old and wear out. You can imagine a protein as a string of different colored beads, each color representing a different amino acid. When the string of beads breaks, we need to build a new one from new beads.

Our bodies make many of these “beads,” or amino acids, on their own, but there are eight they can’t produce. We need to consume these “essential” amino acids in order to replace some of our bodily proteins.

Generally, the amount of protein we need to survive and grow is 5-6% of our calorie intake. However, the average American eats a diet that’s 15-16% protein, three times more than what’s necessary to thrive. 

Protein for Physical Strength and Growth

5-6% of our calories doesn’t sound like very much protein. For centuries, we’ve associated the consumption of animal foods, and the protein in them, with strength, virility, and dominance. Can we meet our growth potential without them?

Researchers have found that consuming more protein is linked to bigger body size. However, 90% of the protein the Chinese ate in one study was plant protein. This plant protein typically made up about 10% of their diet, higher than needed to thrive, but lower than the percentage Americans eat.

Both animal protein and plant protein are linked to greater body weight and body height, but consuming plant protein comes with fewer risks. You can achieve your genetic potential for growth and strength eating solely plant-based foods.

But keep in mind that when consuming plant-based protein, variety matters.

In poor areas where people lacked variety in their food choices, growth was stunted. This was likely due to the prevalence of diseases of poverty and their effect on growth. Eating a variety of plant-based foods minimized both diseases of affluence and diseases of poverty.

All plants contain protein, but foods high in plant-based proteins include soy products, lentils, nuts, seeds, and grains. It’s important to eat a variety of plants since most don’t have all eight essential amino acids. So, for example, rather than getting your protein from lentils at every meal, mix up the types of legumes you eat and pair them with various grains. When wondering, “How much protein do I need?”, remember that you don’t need as much as you think, even if your goal is to build muscle, and you probably don’t need animal protein at all.

Consuming protein is necessary for keeping the body healthy, but can too much protein, more than you need to survive and thrive, actually hurt you?

How Much Protein Is Too Much Protein?

Can you eat too much protein?

We know that the average American eats a diet that’s 15-16% protein, three times more than what’s necessary to thrive. Is this too much protein?

Based on rat studies, this could be a dangerous amount. Not only does eating a lot of animal protein promote cancer growth, but it also displaces other necessary macro- and micronutrients like carbohydrates, vitamins, and minerals. In studies, clusters of cancer cells only developed when rats were fed diets of 12% casein (milk) protein or higher.

What Happens if You Eat Too Much Protein?

Indian Research on Protein and Liver Cancer

There are dangerous, long-term side effects of eating too much protein.

Research out of India involved two groups of rats. Both groups were administered the carcinogen aflatoxin. 

Group 1 ate a diet that was 20% protein (roughly the percentage of protein in the average Western diet).

Group 2 ate a diet that was 5% protein.

Shockingly, every rat eating a 20% protein diet showed evidence of liver cancer and none of the rats eating a 5% protein diet showed evidence of liver cancer.

Researcher T. Colin Campbell was struck by how these findings clarified his hypothesis that protein consumption in the Philippines was somehow related to childhood liver cancer.

Campbell’s Research on Protein and Liver Cancer

Based on the rat study in India and his observations in the Philippines, Campbell developed his own study exploring the relationship between protein and cancer in rats. The program was well-funded for 27 years by respected groups like the National Institutes of Health and the American Cancer Society.

The results both corroborated and expanded on the findings of the Indian study.


  • Low-protein diets kept the carcinogen aflatoxin from causing cancer.
  • Low-protein diets kept tumors from growing.
  • Casein, which comprises 87% of milk’s protein, caused cancer to develop and spread at every stage of growth.
  • Proteins from plants didn’t cause cancer to develop or spread.
  • The percentage of animal-based protein that increased the rate of cancer growth in rats was the same percentage regularly consumed by American humans.

How does eating too much protein, particularly animal protein, cause cancer? There’s evidence that animal proteins let carcinogens into the cell. Carcinogens cause cancer by permanently damaging a cell’s DNA, mutating it from a normal cell to a cancer cell. The cancer cell then replicates, and the cancer may spread to other tissues and body systems.

In the studies, the presence of protein mattered more than the amount of the carcinogen. We can consume large doses of carcinogens and still not get cancer when we limit our animal-protein intake.

Summary of Recommendations

  • Keep your protein intake (especially of animal proteins) at 5-6% of your calorie intake.
  • Consume less animal protein to keep from “activating” the small amounts of carcinogens we unavoidably consume on a daily basis.

Can you eat too much protein? Yes, particularly animal protein. Follow the recommendations below to determine how much protein you need and how much protein is too much protein.

You’re Probably Eating Too Much Protein: How Much is Too Much?

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Like what you just read? Read the rest of the world's best summary of "The China Study" at Shortform. Learn the book's critical concepts in 20 minutes or less.

Here's what you'll find in our full The China Study summary:

  • Why animal proteins (meat, milk) might cause cancer, diabetes, and other diseases
  • Why the medical institution is structured to hide the truth about disease and food
  • The precise diet you'll need to eat to live longer and feel happier

Amanda Penn

Amanda Penn is a writer and reading specialist. She’s published dozens of articles and book reviews spanning a wide range of topics, including health, relationships, psychology, science, and much more. Amanda was a Fulbright Scholar and has taught in schools in the US and South Africa. Amanda received her Master's Degree in Education from the University of Pennsylvania.

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